It has been proposed in the past to use a transparent needle hub of cellulose acetate material molded to a metal cannula as described in U.S. Pat. No. 3,093,134. This transparent hub gave a visual indication of notches, etc. in an embedded rear portion of the cannula corresponding to the beveled forward end of the cannula. Thus, a nurse or physician could determine the cannula's beveled position when the forward end of the cannula was embedded in a patient.
While the above needle hub was transparent, it had a disadvantage in that the cellulose acetate material had a very low deflection temperature, i.e. it would distort at approximately 131.degree. F. The hub could possibly reach such temperatures when left in an automobile on a very hot summer day or in certain sections of a warehouse without air conditioning in certain desert climates. Even if this needle hub only reached temperatures of approximately 120.degree. F., such exposure may slightly vary the dimensions of the hub's internal taper so that it no longer made a good sealing fit with a tapered adapter of a syringe barrel. The applicant has no knowledge that the needle hub described in U.S. Pat. No. 3,093,134 was ever marketed.
Because of the strenuous stresses required in a needle hub that is forcefully wedged onto a syringe barrel, the material of the hub is very critical. Hubs have frequently been made of metal, including aluminum and stainless steel, as well as nylon. Hubs have also been make of polypropylene, but polypropylene hubs are at best only cloudy and translucent with less than 50% light transmission.
The metal hubs which were crimped onto the metal cannula were autoclavable, but were certainly not transparent. The prior nylon hubs were not autoclavable (steam sterilizable) because nylon absorbs substantial amounts of water from the steam and the nylon hubs change dimensions with autoclaving.
A transparent needle hub is highly desirable because it permits the nurse or physician making a puncture into an artery or a vein to observe blood immediately as it arrives at the rear end of the metal cannula. Thus, he can obtain a quicker indication of whether the cannula is properly located in the vein or artery. Previously the blood had to fill the cannula, opaque needle hub, syringe adapter, and enter the main barrel portion before it became visible. Most of the syringe's tapered adapter was covered by the opaque needle hub.
The transparent hub is useful during a hypodermic injection so the nurse or physician can see any air bubbles and expel them before injection. Air bubbles are highly undesirable during injection.
To applicant's knowledge, there has never been a needle on the market which had a hub that is both transparent and autoclavable at temperatures of 240.degree. to 260.degree. F. Needles, such as with metal hubs, are frequently inserted in a tray of assembled instruments in a hospital and the entire tray autoclaved for sterilization immediately prior to surgery.